The present invention relates to a method and a device for estimating an admission pressure in a motor vehicle brake system.
A method for determining a pressure quantity, in particular in a brake system having a delivery pump is described in German Published Patent Application No. 195 28 697. The differential pressure between a first line and a second line is determined on the basis of a quantity that represents a measure of the delivery pump speed.
In addition, German Published Patent Application No. 197 29 097 describes a method for controlling a brake system in which the brake pressure in at least one wheel brake is electrically controlled at least on the basis of the driver""s braking request, with a high-pressure accumulator being provided whose pressure is detected, and with this accumulator pressure being used to control the brake system, whereby, if the accumulator pressure detection system fails, the accumulator pressure is estimated on the basis of a model, and the estimated value is used to control the brake system.
Particularly to ensure the optimum use of a stop control or anti-spin control system (SCS/ASC system), it is advantageous to control intake and discharge valves assigned to a wheel brake cylinder, taking into account the admission pressure, i.e., the pressure between the main brake cylinder and the intake valve. It is possible to detect this pressure with a sensor, although the sensors that can be used for this purpose are very expensive. German Published Patent Application No. 195 28 697 cited above describes a method for estimating the admission pressure on the basis of an accumulator pressure prevailing in an accumulator located at the output end of the wheel brake cylinder. It is assumed in this case that this accumulator pressure is less than the admission pressure, making it possible to use a measured pressure difference to estimate the admission pressure. Disregarding the pressure chamber pressure, however, limits the accuracy of the admission pressure determination to a certain degree.
An object of the present invention is to provide a method and a device, respectively, that can be used to easily determine a or the prevailing admission pressure, i.e., a pressure prevailing between the main brake cylinder and an intake valve of a wheel brake cylinder of a motor vehicle brake system.
Taking into account an admission pressure determined, i.e., estimated, according to the present invention makes it possible to significantly improve an SCS or ASC system. There is no need to provide admission pressure sensors with which numerous conventional SCS/ASC systems are equipped. Further advantages are obtained in connection with a sputter braking action. A sputter braking action occurs when the driver greatly varies the admission pressure by operating the brake pedal. Estimating the admission pressure according to the present invention makes it possible to easily detect this pressure and modify the SCS system accordingly. In LMV-type systems, great advantages for controlling the valves can be achieved by taking into account an admission pressure, and thus also taking into account admission pressure fluctuations.
According to one especially preferred embodiment of the method according to the present invention, the accumulator pressure is determined on the basis of a time that is needed to reduce the pressure in a wheel brake cylinder and to subsequently empty the accumulator. A sufficiently accurate determination, i.e., model, of an accumulator pressure can be obtained on the basis of these easily determinable input quantities. It is also possible to measure the accumulator pressure using suitable sensors.
One particularly preferable approach is for the run-on voltage to be measured as well as modeled on the basis of the determined accumulator pressure and a presettable admission pressure serving as the working point, with the difference between the measured and modeled run-on voltage being viewed as a measure of a difference between the actual admission pressure and the admission pressure serving as the working point.
A working pressure that is determined, i.e., estimated, during one preceding estimate, in particular the immediately preceding estimate, is suitably selected as the admission pressure serving as the working pressure. Highly accurate admission pressure estimates can be obtained by recursively selecting the admission pressure to be used for the model in this manner.
A pressure between 70 and 120 bar, in particular pressures of 80 or 100 bar, is or are preferably selected as the working pressure. These values typically represent occurring admission pressure values, making it possible to determine relatively accurately the difference between the measured and modeled run-on voltage on the basis of a linear relation between the run-on voltage and admission pressure.